1. Industrial Field of the Invention
The present invention relates to a ventilation line opening/closing means of a fuel tank which interrupts a ventilation line extending from the fuel tank to a canister only during fuel supply and opens the ventilation line except for during the fuel supply, so as to limit a fuel level when the fuel tank is full (to prevent overfilling of the fuel).
2. Description of the Prior Art
It has conventionally been performed to prevent over-supplying of fuel into a fuel tank under such a condition that a pressure in the closed fuel tank is increased. In recent years, since air pollution control regulations have been practically enforced, it becomes necessary to perform such modification of design that, in order to effectively remove excessive fuel vapor and to prevent fuel from dispersing in the atmosphere due to an increase of a temperature in the fuel tank, there is provided a ventilation line communicating the fuel tank and a canister.
In a typical example of the fuel tank in which a modification of design demanded from the reinforcement of the air pollution control act is performed and which can restrict the overfilling of fuel, an opening/closing valve is provided in the ventilation line. The opening/closing valve ordinarily operates to open the ventilation line at the time of running of the automobile so as to discharge the fuel vapor to the canister and it operates to shut the ventilation line at the time of fuel supply for the purpose of realizing a closed condition of the fuel tank. A device including the above-described ventilation line is generally called as a ventilation line opening/closing means. Examples of such means have been disclosed in U.S. Pat. Nos. 4,625,777 and 4,706,708.
However, there have been pointed out various disadvantages of the conventional ventilation line opening/closing means.
More specifically, in the ventilation line opening/closing means disclosed in U.S. Pat. No. 4,625,777, a plunger rod for detecting that a filler cap is opened or closed interferes with a fuel supplying operation, or in some cases the plunger rod contacts with a fuel supplying nozzle to actuate the opening/closing valve by mistake. Also, in the means of U.S. Pat. No. 4,706,708, because the opening/closing valve is closed/opened every time the fuel supplying nozzle is inserted/extracted, the closing/opening of the ventilation line is sometimes repeated when the fuel supplying nozzle is inserted into or extracted out of the fuel port at the time of so-called additional fuel supply, so that the limitation of the fuel level raising cannot satisfactorily be performed when the fuel tank is full.
Further, the conventional ventilation line opening/closing means has a complicated structure, and it is difficult to attach the opening/closing valve to the opening/closing means or exchange the valve. An iron filler neck is difficult to be finishedly coated uniformly.